Fibrosis is pathobiological process common to many tissues and diseases which results in tissue remodeling and loss of function, often necessitating organ replacement or leading to end-stage disease. No therapies are currently available that successfully arrest or reverse fibrosis, and this represents a significant unmet clinical need. Fibrosis occurs predominantly in soft tissues (liver, lung, kidney, heart, skin) through fibroblast proliferation and deposition of extracellular matrix. Our recent work in the lung, and that of others in the liver, demonstrates that extracellular matrix stiffening is an early and prominent event in fibrosis. Critically, we and others have found that matrix stiffening from normal to fibroic levels supports fibroblast activation to a proliferative/matrix synthetic state, and the effects of matrix stiffness are independent of (and/or add to) the effects of TGF-beta, the dominant pro-fibrotic soluble factor. Increasing matrix stiffness thus creates a mechanobiological positive feedback loop that drives progressive fibrosis. We therefore believe fibroblast behaviors should be studied in physiologically relevant matrix stiffness conditions to identify new targets for potential therapeutic intervention relevant to fibrosis. To address this need, we have developed a cell culture platform to study fibroblast biology on matrices of stiffness matched to emerging fibrotic lesions in the lung. Importantly, our approach offers the first opportunity to study fibroblast phenotypic responses to molecular screening within a physiologically relevant mechanical environment compatible with a high throughput, discovery oriented approach. We propose here to screen a library of bioactive molecules and measure effects on key disease-relevant cellular phenotypes in a reference lung fibroblast cell line, and then test candidate molecules for their ability to alter fibrogenic activation of disease relevant primary fibroblasts from IPF and control lungs, all on matrices with stiffness matched to emerging fibrotic lesions. Success will be defined by identification of validated hits with broadly functional effects in down regulating fibrogenic activation of disease-related primary human lung fibroblasts. The identification of stiffness-specific therapies could provide new opportunities for targeted deactivation of fibroblasts and move the field toward new approaches for arresting or reversing progressive fibrosis.